In order to study the evolution of the flow pattern in a phase-transition vapor-liquid two-phase flow in a horizontal pipe, numerical simulation based on volume-of-fluid (VOF) model and the Reynolds stress turbulence model (RSM) was performed. The characteristics of convective heat transfer, pressure drop and evolution of flow patterns in the simulated horizontally pipe-flow were analyzed. It was obtained that the VOF model and RSM model can be used to simulate bubble flow, stratified flow, wavy flow, slug flow and annular flow. The simulated two-phase flow patterns are in agreement with the Mandhane flow pattern map. Furthermore, the simulated heat transfer coefficient and pressure drop are also in good agreements with the existing correlations.